The employment minister claims his email has been hacked by campaigners against a Government work experience scheme, which is continuing to attract controversy.

Chris Grayling accused a group of socialist activists of pressuring firms to quit the scheme amid accusations that it was "slave labour" because youngsters worked for nothing, while keeping their benefits.

Supermarket giant Tesco this week offered to pay people on the scheme and asked ministers to remove the threat of benefit sanctions against those not completing their work experience.

Retail giant Poundland has reportedly withdrawn from the scheme after voicing similar concerns about its mandatory element.

Mr Grayling defended the scheme, saying that half of those who joined it after the launch 11 weeks ago had now found a job, often with companies which offered them work experience.

He also claimed that firms reportedly pulling out of the programme, including supermarket giant Sainsbury's, had never formally been involved in the Government initiative because they ran their own scheme. About 100 organisations were involved in the scheme and not one had pulled out, he told BBC Radio 4.

He said a lot of large companies were coming under pressure from Right to Work activists to withdraw from the scheme. Tesco stores have been targeted in the past week, with one in central London having to close last weekend because of a protest.

Mr Grayling claimed his own email address had been hacked by activists demonstrating against Tesco, but he said it was a "false campaign". "It is a small number of activists trying to destabilise companies," he told the programme.

The Socialist Workers Party (SWP) denied it had hacked Mr Grayling's email to tell employers "not to employ slave labour on his workfare schemes".

Charlie Kimber, the party's national secretary, said: "Grayling should know that the campaign against forcing the unemployed to work for nothing is supported by very large numbers of people, not just the SWP. That is why the campaign by Right to Work alongside others has scored successes against several major employers and will continue until the whole scheme is scrapped."